The present invention relates to a pulse generator for the spark erosive machining of a conductive workpiece.
A wide variety of pulse generators are used in spark erosion technology. Those with a high efficiency are particularly sought in production technology where power costs, heat production, and equipment size should be minimized.
Although many types of pulse generator are already known for spark erosive machining, all of them suffer from disadvantages, so that improvements in efficiency cannot readily be obtained. Pulse generators are also known which no longer use the previously conventional load resistors for power regulation purposes. One such device is disclosed by German Pat. No. 2,747,767, which describes a generator circuit that can supply randomly shaped current pulses in that a regulating device ensures the pulse current is always in the area between two given envelope curves.
This circuit would be suitable for achieving efficiencies over 60%, but suffers from the disadvantage that high no-load voltages at the spark gap can only be obtained by switching in pulse generators with load resistors. The sharp pulses required by the technology also call for a rapid disconnection device, which in turn takes up all the energy to be dissipated in a load resistor. Thus, the overall efficiency of such pulse generators is undesirable.
German Pat. No. 2,735,403 discloses a pulse generator for wire cutting, which in the case of particularly short pulses of 1 microsecond and less can supply high pulse currents of several hundred amperes. Although this generator type permits a high productivity and high precision, in the case of the conventional design employing a d.c. voltage source of approximately 300 V, the generator efficiency is well below 10% due to the load resistors present. Such an efficiency level is unacceptable for more extensive use in production installations.